Illustrative Examples

Description

Illustrative Examples

For purposes of illustration the logs of five of the eleven holes whose cost was given on page 16 are given on page 19.

Elevation of water in river - 89 to 90. Considering the character of the rock and the conditions under which some of the borings were made, the percentages of core recovered may be considered as high. For boring No. 1 the machine was set directly on the rock while the others were made from a suspended bridge or staging.

A streak of somewhat softer rock, occurring no doubt below the bottom of Hole No. 1, is indicated in Hole No. 2, between elevations 45 and 52, at about the same elevation in Hole No. 3; at Hole No. 5, next in line, the soft streak occurs at 56.5 to 63; finally, in Hole No. 4, at 65 to 71. A careful examination of the stratification exposed in the canyon walls showed that such a change of elevation was entirely consistent.

In each case, it will be observed, the boring proceeded through the soft streak with a smoothness that required no frequent withdrawals of the core. In the case of Hole No. 3 the 8.17 ft. of penetration might have yielded more core if it had been withdrawn often, but it shows distinctly different rock from the 8.0 ft. penetration above which yielded 6.16 ft. of core. Similarly in Hole. No. 5 the 6.40 penetration yielding 2.20 ft. of core shows a different kind of rock than the 9.42 ft. of penetration yielding 8.50 ft. of core. The first three measurements in Hole No. 5 simply show slight inaccuracies of measurement, either of the penetration or of the assembled pieces of core. In Hole No. 4 (accepting the measurements as correct) the first ten measurements arrived at the soft streak with a loss of only 0.20 ft. of core; the last three measurements show that more than a foot of core must have been left in the hole when the 4.80 was withdrawn.